1. Field of the Invention
The present invention relates to an apparatus for converting image format and methods thereof in a video signal processing system, and more particularly, to an image format converting apparatus and methods thereof by which a converted image of first-rate quality is realized when horizontal and vertical dimensions of an image are converted at any rate and at the same time, and the amount of hardware and computation necessary for an image conversion can be reduced.
2. Description of the Related Art
Generally, the term "multimedia" refers to a system which can transmit information relating to characters, pictures, audio and the like and is applied to televisions, computers, videophones, and the like.
It is necessary to convert the format of a video signal during interface processing in multimedia applications in which systems of different types are combined together into a system. Such combinations could include a personal computer connected to another personal computer, a personal computer connected to a television, a television connected to a television, etc.
An example of such image format conversion is conversion of an image from 500.times.400 resolution to 300.times.300 resolution; in this case, the horizontal scale-down ratio is 5 to 3 and the vertical scale-down ratio is 4 to 3.
This is basically achieved by converting such time factors as horizontal and vertical frequency, pixel frequency and the like and such dimensional factors as the horizontal and vertical size of an image.
Then the time factor-conversion is realized by using a memory buffer and the dimensional factor-conversion is realized by using filters.
For example, when five image samples are input in order to scale down an image in the ratio of 5 to 3, three image samples have to be produced.
According to the conventional format-converting method, the number of samples is interpolated by 3 to be increased by a factor of three, and then is decimated by 5 to be decreased by a factor of 1/5.
Using this process, interpolations and decimations each have to be carried out more than 30 times.
Meanwhile, according to the conventional image format-conversion method using hardware, lines (verticality) or pixels (horizontality) are skipped at predetermined intervals to scale down the image in size, and lines (verticality) or pixels (horizontality) are folded at predetermined intervals to scale up the image in size.
Such conventional methods allow the hardware to be easily realized, but there is a problem in that the image appears coarse, and in particular, characters appear broken in the case where a PC image containing many characters is scaled-down.
Conventional methods require a filter having a number of taps to prevent the quality of an image from deteriorating when converting image format; n-1 line memory units are needed when a filter having n taps is used for scaling in a vertical direction.
Accordingly, there is a disadvantage with the conventional method thus performed because it is expensive to manufacture hardware capable of providing a high quality image when performing an image format conversion.